Spam is a big problem. People get tired of seeing one bogus offer after another show up in their email inboxes. So, they and their service providers use sophisticated filters to separate the wheat from the irritating chaff.

Unfortunately for legitimate marketers, often consumers and anti-spam technology don't see much difference between a legitimate marketing message and a Nigerian scam email. How often? A study by email analytics firm Return Path reports that at least 16% of commercial emails never reach their intended inboxes.

Marketers end up with bad reputations among ISPs for two main reasons. One is spam complaints. Indiscriminate or sloppy tactics can be indistinguishable from shadier pitches in consumers' minds--it all looks like unwanted mail. So they mark it as spam in an effort to avoid similar emails in the future.

The other reason is spam traps. A spam trap is an inactive email address that should get no messages. The address may be one that an ISP explicitly set up for the purpose, or it might be an abandoned account. ISPs assume that mail reaching such accounts must be spam. However, real mail from marketers makes up 70% of spam complaints and 60% of spam-trap hits, although marketing mail comprises only 18% of total email volume. Even botnets cause only 3% of complaints and 11% of spam-trap hits.

Return Path examined 315,000 campaigns run by its clients to track how many emails went missing, were received successfully, and were caught by an ISP in a spam folder. Although the study is not necessarily statistically representative of all marketers--there may be characteristics of the companies using Return Path that are unusual, and the firm didn't specify how many companies were responsible for the total number of campaigns--it is enough data to make you consider whether it should apply to you, as well.

According to Return Path, there are three things marketers should do that many don't:

Pay attention to and track email complaints

Discover the underlying causes for email not going through

Confirm continued interest on the part of people receiving marketing email

Ignore these three important steps to managing email and you may find that your newsletters, offers, and other messages also disappear into the Great Spam Void.

The opinions expressed here by Inc.com columnists are their own, not those of Inc.com.